Despite the crew's efforts, the 707 entered a violent porpoising motion, alternating abrupt pitch-up and pitch-down movement.

[2] While continuing descent to 11,000 feet (3,400 m), the crew notified the air traffic control of an emergency and contacted the TWA maintenance center.

Two flight attendants strapped in their seats and three passengers, standing or moving in the aisles, were injured, requiring hospitalization.

[2] Combining the increased waviness of the left elevator with its slight misalignment, the boundary layer of air over the elevator in flight was thicker than in other 707s, which caused its hinge moment to be much lower; in simpler terms, on N8705T the layer of air flowing over the left stabilizer was thicker than on other aircraft because two effects combined together: the increased waviness of the metal skin and the slight misalignment of the stabilizer–elevator assembly.

[2][3] In flight, the balance of the 707 is constantly changing as fuel burns and weight decreases; an automatic system is designed to keep the plane in trim.

On August 28, 1973, as the plane was descending towards Los Angeles, this out of trim situation caused an abrupt pitch-up of the aircraft.

The crew tried to push the nose down, unknowingly making the situation worse: They used the amount of force and forward deflection of the control column that they were accustomed to on other 707s and which assumed to be enough to bring the plane back to level flight.

Trying to rectify that, they pulled the yokes back, but once again, they unknowingly used too much force, over-corrected, and caused yet another violent pitch-up instead of leveling off.

The investigators noted that the majority of the injuries sustained on Flight 742 were caused by presence of sharp and misplaced objects in the cabin; they called for inspection and redesign of the interiors and galleys on a commercial aircraft (padding hard surfaces, elimination of sharp edges and corners, improved locks in overhead luggage racks) to avoid accidental injuries when encountering turbulences.